Cannot find camera after deleting and appending a new one with python
If the new camera is getting named Camera.001 then it is likely that the old camera is not being deleted, as blender appends .XXX (where XXX is some number) when the requested name is already in use. I'm not to familiar with all the python delete functions, but this could be because that data isn't actually deleted until the scene is saved and re-opened, due to how blender manages garbage collection/scene data. 

You probably need to update your script to get the name of the new camera from ti after creation or assign a unique name to it when you create it, and the use that to set the active camera